The present invention relates to a composite staple fiber having a cross-section in which two polymer components are alternately layered. More particularly, the present invention relates to a composite staple fiber having its outer surface covered with one of the polymer components that constitute the fiber. More specifically, the present invention relates to a composite staple fiber which does not cause peeling or splitting between layered polymer components in the carding or needle punching treatment of a non-woven fabric production, but causes cracking in the surrounding polymer in the subsequent dividing and splitting process by a water jet treatment, a buffing treatment, etc., and then causes peeling and splitting between the layered polymer components inside the fiber, thereby allowing to obtain a fiber structure composed of groups of ultrafine fibers of the polymer components.
Since a part of the surrounding polymer of the composite staple fiber is broken in the dividing and splitting process to result in the formation of ultrafine fibers having acute edges, the fiber structure exhibits a superior wiping capacity when used, for example, as a wiper. In addition, since the fiber structure contains ultrafine fibers, artificial leather, spun lace and non-woven fabric for sanitary use having soft texture and satisfactory permeability are obtained. Moreover, since composed of densely packed fibers, the fiber structure has a good water absorption by capillary action, and shows a superior dust-removing performance when used as a filter, a breathing mask, etc. Moreover, sheets made of divided and split composite staple fibers, or sheets obtained by dividing and splitting composite staple fiber sheets have their own characteristic luster due to the flat, ultrafine fibers formed by splitting.
Since there are limitations on the fiber fineness due to increased susceptibility to breakage during a direct spinning, ultrafine fibers having a single fiber fineness of 0.1 denier or less have been produced by a conjugate spinning method. Examples of the cross-section of the composite fibers for forming ultrafine fibers include: (1) a multi-layered cross-section or a petal-shaped cross-section in which many parts of respective two components are separately and mutually arranged in layers, and (2) an islands-in-a-sea cross-section in which one component is finely dispersed in another component. In the former composite fibers, ultrafine fibers having sharp edges and ultrafine fibers having modified cross-sections are formed by the peeling of the components, and find various applications depending on their shapes.
Such composite fibers are typically composed of Nylon 6 and polyethylene terephthalate (PET). The methods for peeling and dividing these components include (1) a method of separation by shrinking force of the Nylon component when treated with a liquid containing a chemical such as benzyl alcohol, (2) a method of separation by slightly dissolving away the PET component with an aqueous alkali solution, (3) a method of peeling by repeating wet heat treatment and drying treatment several times, (4) a method of forcible separation by physically scouring or rubbing, and (5) a combination thereof.
It is important in view of productivity to prevent the generation of fluff caused by peeling between the composite components during the fiber production process such as the drawing process. Therefore, in a combination of, for example, Nylon 6 and PET, a PET copolymerized with 5-sodium sulfoisophthalate is used to improve the adhesion between the components. Alternatively, it has been proposed to prevent the peeling during the fiber production by spinning the composite fiber at such an increased spinning speed as to make PET and Nylon to show similar shrinkage behaviors.
However, even in the case of employing the above measures against the fiber splitting, the peeling occurs between the components of the composite fiber in the carding process for producing non-woven fabrics or spun yarns from staple fibers, resulting in the problems of the splitting composite fiber and the generation of neps. In addition, when the needle punching is performed to entangle the fibers, the peeling due to damage occurs to make composite fibers resistant to entanglement, thereby resulting in the problem of failure to increase the peel strength of the non-woven fabric.
For example, Japanese Patent Application Laid-Open Nos. 4-308224 and 5-44127 propose to prevent the peeling and splitting between the components during the carding process of the subdividable composite fiber by covering the fiber surface with one of the components that compose the composite fiber.
However, these known techniques are directed to composite fibers of a type in which the surrounding of the composite fibers is dissolved away after made into fabrics by the treatment with a solvent, and do not disclose in any way a composite staple fiber having a surrounding that is not broken during the carding or needle punching process, but broken in the subsequent dividing and splitting process such as water jet treatment, etc. to cause the composite staple fibers to be subdivided into ultrafine fibers.
In addition, in the technique described in Japanese Patent Application Laid-Open No. 4-308224, since ultrafine fibers are formed by dissolving away the surrounding made of one of the components that encapsulates the other component, the yield of ultrafine fibers is low, resulting in the problem of poor production efficiency of ultrafine fibers. In addition, it is difficult to control the surrounding thickness to a desired level simply by changing the proportion of both components. The proposed technique is adequate for forming ultrafine fibers by entirely dissolving away one of the components with solvent, etc. However, not suitable for allowing both the components to remain as ultrafine fibers by a mechanical processing method, because the surrounding of the proposed technique is excessively thick thereby preventing the composite fibers from being split adequately.
Japanese Patent Application Laid-Open No. 5-44127 discloses composite long fibers for constituting composite pre-twisted yarns, and proposes a technique for inhibiting the fibrillation of composite fibers due to friction during a pre-twisting process by covering with polyester the surface of the composites long fibers having a polyamide-polyester layered structure. However, it is only described that, after making the composite pre-twisted yarn into a woven or knitted fabric, the covering polyester is dissolved away by alkali treatment, thereby dividing the composite components. Thus, there is no description of a composite staple fiber which is resistant to the peeling during the carding and the needle punching treatment of a non-woven fabric production, etc., but is subdivided into ultrafine fibers by the subsequent mechanical peeling and dividing process such as water jet treatment.
An object of the present invention is to provide a composite staple fiber and a production method thereof, in which there is substantially no occurrence of the peeling or splitting between the components that compose the composite fiber during the carding process, the needle punching process, etc., in the production of non-woven fabrics, etc., but the peeling and splitting between the composite components occur only in a subsequent physical dividing process such as a water jet treatment. Another object of the present invention is to provide a fiber structure that contains the above composite staple fiber and shows a superior wiping performance when used as a wiper. Still another object is to provide a fiber structure that contains the above composite staple fiber and exhibit a satisfactory texture and satisfactory color development when used as artificial leather.
Namely, in a first aspect of the present invention, there is provided a composite staple fiber having a layered composite structure in which a polymer component A and a polymer component B are alternately arranged in a fiber cross-section, wherein the polymer component B is completely covered with the polymer component A, the polymer component B and a portion of the polymer component A except for the skin-forming portion has a substantially flat shape, and in the fiber cross-section, the ends of the polymer component B in the lengthwise direction are located 0.05 to 1.5 xcexcm inside the fiber surface, and a weight ratio of the polymer component A to the polymer component B is from 90/10 to 10/90.
In a second aspect of the present invention, there is provided a process for producing a composite staple fiber having a layered composite structure in which a polymer component A and a polymer component B are alternately arranged in a fiber cross-section, wherein the polymer component A and the polymer component B are melt-spun so that a solubility parameter, SP value, and a melt viscosity during the melt-spinning of each component satisfy the following Equation 1:
xcex7Axe2x88x92xcex7Bxe2x89xa6xe2x88x92200xc3x97(SPAxe2x88x92SPB)xe2x80x83xe2x80x831
wherein xcex7A is a melt viscosity (poise) of the polymer component A during the melt-spinning, xcex7B is a melt viscosity (poise) of the polymer component B during the melt-spinning, SPA is a solubility parameter of the polymer component A, and SPB is a solubility parameter of polymer component B.
FIG. 1 is a cross-sectional view showing an example of the composite staple fiber of the present invention;
FIG. 2a is a cross-sectional view of a flat ultrafine fiber composed of a polymer component A, formed by dividing a composite staple fiber; and
FIG. 2b is a cross-sectional view of a flat ultrafine fiber composed of a polymer component B, formed by dividing a composite staple fiber.